Characterization of carbohydrate oxidation at copper electrodes

Abstract

The electro-oxidation of carbohydrate compounds at copper electrodes in strongly alkaline solution was investigated by cyclic voltammetry, hydrodynamic voltammetry and coulometry experiments. Product analysis was carried out by 1H and 13C nuclear magnetic resonance spectroscopy. Model carbohydrate compounds examined included, in addition to simple monosaccharides, alditols and aldonic, aldaric and uronic acids. All these oxidations were found to consist of many-electron processes. For glucose itself, 12 electrons were involved in complete oxidation at +0.60 V vs. Ag|AgCl|3 M NaCl, and the sole product appeared to be the formate ion, with no partial oxidation species seen as either intermediate or final products. For other carbohydrates, carbonate was assumed (but not observed) to be a possible oxidation product as well. In view of the fact that various alditol compounds were oxidized even more readily than glucose and other monosaccharides, it appeared that the aldehyde or ketone functionality is not required for oxidation at the Cu electrode. Rather, voltammetry results obtained for a series of polyhydroxyl compounds revealed that the minimum structural requirement for facile oxidation is the presence of at least two, and preferably more, nearby hydroxyl groups in the compound to be oxidized.